1. Field of the Invention
The present invention relates to a technique capable of identifying the position of an identification object from image data and displaying the identification object position on an image produced based on the image data.
2. Description of the Related Art
A conventional technique can register feature data representing a main shooting subject (i.e., an identification object satisfying predetermined conditions) beforehand, and identify the main shooting subject based on a comparison between captured image data and the registered feature data.
For example, as discussed in Japanese Patent Application Laid-open No. 09-251534, a face region can be identified based on correlation values between image data of an identification object and pre-registered face image data.
Furthermore, as discussed in Japanese Patent Application Laid-open No. 10-162118, image data can be divided into a plurality of frequency band components and a face region can be estimated. Then, correlation values between the estimated face region and pre-registered face image data can be calculated. These techniques are applicable to a camera.
For example, Japanese Patent Application Laid-open No. 2003-107335 discloses a camera that can automate the processes of detecting a main shooting subject from obtained image data using a shape analysis, displaying a focus detection area corresponding to the detected main shooting subject, and performing a focus adjustment action applied to the focus detection area.
As discussed in Japanese Patent Application Laid-open No. 2004-317699, a face region (i.e., main shooting subject) can be identified by extracting feature points from image data and a focus detection area can be set according to the size of the identified region.
Moreover, as discussed in Japanese Patent Application Laid-open No. 2004-320286, a face region can be identified by extracting feature points from image data and a zoom control can be performed based on the size of the identified region.
In general, a region identifying a main shooting subject (hereinafter, referred to as “identified region”) can be displayed to enable a user to easily check a shooting subject identified from image data.
According to the above-described Japanese Patent Application Laid-open Nos. 2003-107335 and 2004-317699, a face frame surrounding the identified region can be displayed to let a user recognize the identified face region.
If a main shooting subject is moving, it is useful to periodically detect a main shooting subject and update a frame indicating an identified region (hereinafter, referred to as “object identification mark”). More specifically, if a main shooting subject is shifting, the mark can be momentarily updated to follow up the moving shooting subject. When the update period of the mark is short, the mark can speedily follow up the shooting subject although the response is dependent on a calculation speed.
However, the following problems will arise if the update period of the mark is short. For example, when a main shooting subject (i.e., object) is walking or running, the main shooting subject causes an up-and-down motion as shown in FIG. 14. In general, human eyes can easily recognize a lateral (advancing) shift motion of a walking or running subject.
However, it is difficult to recognize an up-and-down motion of a walking subject. For example, if a human face is set as a main shooting subject and the update period is short, the mark indicating a walking or running subject will frequently swing in the up-and-down direction as shown in FIG. 15. The display of an image frequently swinging in the up-and-down direction is not similar to actual recognition by a user and unnatural for a user to view.
To overcome the above-described problem, the update period of the mark can be enlarged. However, if the update period is long, a user may feel that the mark cannot smoothly follow up a moving object. Moreover, if a shift distance of a main shooting subject is short, it may be desirable to fix the mark. However, the mark does not start shifting before the main shooting subject shifts a certain distance. Thus, a user may feel that the mark cannot smoothly follow up a moving subject.
Therefore, to improve the visibility of the mark, the movement of the mark indicating an identified region of a main shooting subject is required to naturally follow up the movement of a main shooting subject recognized by a user.